Methods of Forming Epitaxial Structures in Fin-Like Field Effect Transistors

ABSTRACT

A method of fabricating a fin-like field effect transistor (FinFET) device includes providing a semiconductor substrate having a region for forming p-type metal-oxide-semiconductor (PMOS) devices and a region for forming n-type metal-oxide-semiconductor (PMOS) devices, forming fin structures in both regions of the substrate separated by isolation features, first forming source/drain (S/D) features in the PMOS region, and subsequently forming S/D features in the NMOS region. First forming the PMOS S/D features and then forming the NMOS S/D features results in a greater extent of loss of isolation features in the PMOS region than in the NMOS region.

PRIORITY

This application is a divisional application of U.S. patent applicationSer. No. 15/939,647 filed on Mar. 29, 2018, which claims priority toU.S. Provisional Patent Application Ser. No. 62/589,664 filed on Nov.22, 2017, the entire disclosure of which is hereby incorporated hereinby reference.

BACKGROUND

The integrated circuit (IC) industry has experienced exponential growth.Technological advances in IC materials and design have producedgenerations of ICs, where each generation has smaller and more complexcircuits than the previous generation. In the course of IC evolution,functional density (i.e., the number of interconnected devices per chiparea) has generally increased while geometry size (i.e., the smallestcomponent (or line) that can be created using a fabrication process) hasdecreased. This scaling down process generally provides benefits byincreasing production efficiency and lowering associated costs.

Such scaling down has also increased the complexity of processing andmanufacturing ICs and, for these advances to be realized, similardevelopments in IC processing and manufacturing are needed. For example,planar transistors have been replaced by three-dimensional fin-likefield effect transistors (FinFET) for which the n-type source/drainfeatures and the p-type source/drain features are often formed inseparate processes in an effort for improving device performance withdecreased feature size. However, there are challenges associated withthis fabrication method. In one example, due to structural differencesbetween the n-type and p-type source/drain features, the sequence bywhich these features are formed may be improved upon to accommodate thefabrication of devices with reduced feature sizes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1A-1B illustrate a flowchart of an exemplary method forfabricating a semiconductor structure according to various aspects ofthe present disclosure.

FIG. 2 is a perspective, three-dimensional views of the semiconductorstructure according to various aspects of the present disclosure.

FIGS. 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and 16 are fragmentarycross-sectional views of a FinFET device along line AA′ as shown in FIG.2 and according to various aspects of the present disclosure.

FIG. 5 is a fragmentary cross-sectional view of a semiconductorstructure along line BB′ as shown in FIG. 2 and according to variousaspects of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact.

In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “over,” “below,” “beneath,”“up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for easeof the present disclosure of one features relationship to anotherfeature. The spatially relative terms are intended to cover differentorientations of the device including the features.

The present disclosure relates generally to methods for fabricatingsemiconductor devices, and more particularly to methods of formingsource/drain features in fin-like field effect transistor (FinFET)devices. The FinFET devices, for example, may be complementarymetal-oxide-semiconductor (CMOS) devices comprising a p-typemetal-oxide-semiconductor (PMOS) FinFET device and an n-typemetal-oxide-semiconductor (NMOS) FinFET device. In fabricating CMOSFinFET devices comprising both NMOS and PMOS devices, source/drain (S/D)features of the NMOS device are oftentimes formed separately from S/Dfeatures of the PMOS device. In particular, the S/D features of the NMOSdevice are usually formed first, followed by the formation of the S/Dfeatures of the PMOS device. This may be accomplished by firstprotecting (by, for example, a photoresist layer) the region of theFinFET providing the PMOS device, and then recessing the fins in theregion of the FinFET providing the NMOS device before forming the NMOSS/D features on the recessed fins. Thereafter, the NMOS S/D features aresimilarly protected to accommodate the formation of the PMOS S/Dfeatures. However, because the NMOS S/D features differ from the PMOSS/D features in many respects, forming the NMOS S/D features beforeforming the PMOS S/D features poses challenges in subsequent processes.For example, the NMOS S/D features generally have larger size (e.g.,features merging multiple fins) and structural variations than the PMOSS/D features; thus, forming the NMOS S/D features first leaves a smallprocessing window for the subsequent fabrication of the PMOS S/Dfeatures, which may cause poor feature uniformity, potentialphotolithography misalignment, and/or other adverse effects.Accordingly, the present disclosure contemplates methods of forming PMOSS/D features before forming NMOS S/D features in order to enlarge theoverall process window.

FIGS. 1A-1B illustrate a flowchart of method 100 for fabricating FinFETdevices in an exemplary semiconductor structure according to someaspects of the present disclosure. A portion of the exemplarysemiconductor structure 200 according to aspects of the presentdisclosure is depicted in FIG. 2 to aid the discussion of the varioussteps of method 100. The semiconductor structure 200, as shown in FIG.2, includes a semiconductor substrate 110, a plurality of fins 120 (oralternatively, “active regions”) disposed in a first region 140 and asecond region 150 of the semiconductor substrate 110 and separated byisolation features 130, a dummy gate structure 160 that includes variousmaterials layers such as, for example, a dummy gate dielectric layer 162and a dummy gate electrode layer 164. Additional devices and features,though not shown, may also be present in the semiconductor structure 200and any variations thereof according to aspects of the presentdisclosure.

The method 100 is described with respect to cross-sectional views of thesemiconductor 200 in a source/drain (S/D) region taken along directionAA′ (FIGS. 3, 4, and 6-16) and in a channel region taken along directionBB′ (FIG. 5). Various aspects of the present disclosure provide that thechannel region and the S/D region of the semiconductor structure 200undergo substantially similar processes during operations 70 and 72, andthe channel region remains largely unaffected during operations 76-94applied to the S/D region. Accordingly, a portion of the cross-sectionalview along the direction BB′ of the channel region is only depicted inFIG. 5. Additional steps can be provided before, during, and after themethod 100, and some of the steps described can be replaced, eliminated,or moved around for additional embodiments of the method 100.

At operation 70, the method 100 (FIG. 1A) provides a semiconductorsubstrate 110. The substrate 110 includes an elementary semiconductorhaving a crystalline structure, such as silicon. Alternatively oradditionally, the substrate 110 includes another elementarysemiconductor, such as germanium; a compound semiconductor includingsilicon carbide, gallium arsenide, gallium phosphide, indium phosphide,indium arsenide, and/or indium antimonide; an alloy semiconductorincluding silicon germanium, gallium arsenide phosphide, aluminum indiumphosphide, aluminum gallium arsenide, gallium indium arenside, galliumindium phosphide, and gallium indium arsenide phosphide; or combinationsthereof. Alternatively, the substrate 110 may be asemiconductor-on-insulator substrate, such as a silicon-on-insulator(SOI) substrate, a silicon germanium-on-insulator (SGOI) substrate, or agermanium-on-insulator (GOI) substrate. Semiconductor-on-insulatorsubstrates can be fabricated using separation by implantation of oxygen(SIMOX), wafer bonding, and/or other suitable methods. The substrate 110may further include features such as a buried layer, and/or an epitaxialsemiconductor layer grown in its upper portion. In the depictedembodiments, the substrate 110 includes a first region 140 (a PMOSregion) and a second region 150 (an NMOS region).

In some embodiments, additional material layers (not shown) such as ahard mask layer and a resist layer are formed over the substrate 110during step 70 to facilitate subsequent steps of method 100 to form fins120. In some embodiments, the hard mask layer may include any suitablematerial, such as silicon oxide, silicon nitride, silicon carbide,silicon oxycarbide, silicon oxynitride, spin-on glass (SOG), a low-kdielectric material, tetraethylorthosilicate (TEOS), or other suitablematerials, and may be formed by a suitable method, such as thermaloxidation, chemical vapor deposition (CVD), physical vapor deposition(PVD), atomic-layer deposition (ALD), other suitable methods, or acombination thereof. The resist layer may include, for example, aphotosensitive material that causes the resist layer to undergo changesin chemical properties when exposed to light. The resist layer can beformed by a process such as spin coating over the hard mask layer. Themethod 100 may use a series of photolithography and etching processes topattern the hard mask layer to form fins 120 over the substrate 110 asdiscussed in detail below.

At operation 72, the method 100 (FIG. 1A) forms fins 120 in the firstregion 140 and the second region 150. As illustrated in FIG. 3, the fins120 are formed over the substrate 110 and separated by isolationfeatures 130. In some embodiments, forming the fins 120 also leads tothe formation of isolation features 130. In some embodiments, theisolation features 130 include, for example, silicon oxide, siliconnitride, silicon oxynitride, fluorine-doped silicate glass (FSG), alow-k dielectric material, other suitable dielectric materials, orcombinations thereof. The isolation features 130 can include differentstructures such as shallow trench isolation (STI) structures, deeptrench isolation (DTI) structures, and/or local oxidation of silicon(LOCOS) structures.

The fins 120 and the isolation features 130 can be formed by anysuitable process. In an exemplary embodiment, the process can includethe following steps: one or more processes for patterning the hard masklayer discussed above (e.g., by using the patterned resist layerdiscussed above) over the substrate 110, an etching process (e.g., a dryetching and/or wet etching process) to etch trenches in the substrate110 not covered by the patterned hard mask layer, and a depositionprocess (e.g., a chemical vapor deposition process and/or a spin-onglass process) to fill in the trenches with one or more insulatingmaterials to form the isolation features 130. The trenches may bepartially filled, where the substrate remaining between trenches formsthe fins 120. The hard mark layer may be patterned using one or morephotolithography processes, including double-patterning ormulti-patterning processes. Generally, double-patterning ormulti-patterning processes combine photolithography and self-alignedprocesses, allowing patterns to be created that have, for example,pitches smaller than what is otherwise obtainable using a single, directphotolithography process. For example, in one embodiment, a sacrificiallayer is formed over the substrate 110 and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers, or mandrels, become thepatterned hard mask layer. Following the formation of the fins 120, thehard mask layer and the resist layer are removed.

Alternative to partially filling the trenches with the insulatingmaterial, operation 72 may completely fill the trenches with theinsulating material, planarize a top surface of the filled trenches toremove any excessive insulating material using, for example, a polishingprocess such as chemical mechanical polishing/planarization (CMP), andselectively grow one or more layers of epitaxial semiconductor materialsover the exposed substrate 110 thereby forming the fins 120 withisolation features 130 disposed in between the fins 120. The epitaxialsemiconductor material can be silicon, germanium, silicon germanium,other suitable materials, or combinations thereof. Accordingly, the fins120 formed by embodiments provided herein may comprise the same materialas the substrate 110 or, alternatively, they may comprise one or morelayers of epitaxially grown semiconductor materials over the substrate110. In the depicted embodiments, the fins 120 comprise the samematerial as the substrate 110.

At operation 74, the method 100 (FIG. 1A) forms a first hard mask layer410 over the fins 120 (i.e., the first fin structure 122 and the secondfin structures 124) and the isolation features 130 in both the firstregion 140 and the second region 150, as shown in FIG. 4. The first hardmask layer 410 acts as a barrier between the fins 120 and thesubsequently formed patterned etch mask 610 (FIG. 6) to avoidcontaminating the fins 120. In some embodiments, the hard mask layer 410includes any suitable material, such as silicon oxide, silicon nitride,silicon carbide, silicon oxycarbide, silicon oxynitride, SOG, a low-kdielectric material, TEOS, or other suitable materials, and may beformed by a suitable method, such as thermal oxidation, CVD, PVD, ALD,other suitable methods, or a combination thereof.

In the depicted embodiments, the first fin structure 122 comprising onefin 120 forms PMOS FinFET devices and the second fin structure 124 eachcomprising two fins connected at the bottom forms NMOS FinFET devices.As such, the first region 140 is hereafter referred to as the “PMOSregion” and the second region 150 is hereafter referred to as the “NMOSregion.” Although the depicted embodiments of FIG. 3 and the subsequentfigures show four fins 120 disposed in the NMOS region 150 and one fin120 in the PMOS region 140, embodiments of the present disclosure arenot limited to this configuration. For example, there may be two finsformed in the NMOS region 140 rather than four fins as depicted herein.

At operation 76, the method 100 (FIG. 1A) forms a dummy gate structure160 over the isolation features 130 and engaging the fins 120 asdepicted in FIG. 5. In some embodiments, additional dummy gatestructures may be formed separately in the PMOS region 140 and the NMOSregion 150. FIG. 5 illustrates a cross-sectional view of the channelregion of the dummy gate structure 160 taken along the direction BB′ asshown in FIG. 2. As depicted herein, the dummy gate structure 160includes a dummy gate dielectric layer 162 and a dummy gate electrodelayer 164 comprising polysilicon. In various embodiments, the dummy gatestructure 160 may include additional layers such as interfacial layers,capping layers, diffusion and/or barrier layers, dielectric layers,conductive layers, other suitable layers, and/or combinations thereof.The dummy gate structure 160 may be formed by deposition and etchingprocesses.

In some embodiments, gate spacers (i.e., sidewall spacers; not shown)are formed on each side of the dummy gate structure 160. The gatespacers may comprise a dielectric material, such as silicon oxide,silicon nitride, silicon oxynitride, silicon carbide, other dielectricmaterial, or combinations thereof, and my comprise one or multiplelayers of material. The gate spacers may be formed by depositing aspacer material as a blanket over the isolation features 130, the fins120, and the dummy gate structure 160. Subsequently, the spacer materialis etched back anisotropically during an etching process. Portions ofthe spacer material on the sidewalls of the dummy gate structures remainand form the gate spacers (not shown).

In the depicted embodiments, portions of the dummy gate structure 160are subjected to a high-k metal gate (HK MG) replacement process afterhigh thermal budget processes are performed. In some embodiments, thedummy gate electrode 164 is replaced with a plurality of metal layers toform a conductive electrode, while the dummy gate dielectric layer 162is replaced with a high-k gate dielectric layer.

At operation 78, as depicted in FIG. 6, the method 100 (FIG. 1A) forms apatterned etch mask 610 over the first hard mask layer 410 and theisolation features 130 in the NMOS region 150, thereby exposing the PMOSregion 140 to subsequent fabrication processes. In an embodiment, thepatterned etch mask 610 includes a patterned resist layer. The resistlayer may include, for example, a photosensitive material that causesthe resist layer to undergo changes in chemical properties when exposedto light. The resist layer can be formed by a process such as spincoating over the first hard mask layer 410.

Thereafter, at operation 80, the method 100 (FIG. 1A) recesses a portion710 of the first fin structure 122 in the PMOS region 140 while thepatterned etch mask 610 covers the NMOS region 150. The recessingprocess may include a dry etching process, a wet etching process, othersuitable etching process, or combinations thereof. In some embodiments,a reactive ion etching (RIE) process is performed. In the depictedembodiments, a dry etching process is implemented to recess the fin 120.After recessing the fin 120, the patterned etch mask 610 is removed fromthe PMOS region 140.

In some embodiments, the dry etching process is implemented to removethe portion 710 of the first fin structure 122 in the PMOS region 140.The dry etching process may utilize one or more etchant comprisingfluorine, bromine, sulfur, carbon, oxygen, and/or hydrogen atoms. Insome embodiments, the dry etching process implements a mixture ofetchant gasses comprising CF₄, SF₆, CH₂F₂, CHF₃, C₂F₆, Br, and/or O₂. Insome embodiments, a bias voltage is applied during the dry etchingprocess to increase the anisotropy of the dry etching process.

As depicted in FIG. 7, recessing the first fin structure 122 in the PMOSregion 140 also removes portions of the isolation features 130 in thevicinity of the first fin structure 122 and forms a recessed region 730Aand a recessed region 730B in the isolation features 130 on each side ofthe S/D feature 810. In some embodiments, the recessed region 730A isdefined by a vertical distance 720 between a top surface 760 of theisolation features 130 prior to the recessing process and the lowestpoint 740 of the isolation features 130 in the recessed region 730A. Insome embodiments, the lowest point 740 of the isolation feature 130(i.e., the lowest point of the recessed region 730A) is adjacent to aninterface between the lowest point of the S/D feature 810 and a topsurface of the recessed first fin structure 122. In some embodiments,the lowest point 740 is at about the same height as a top surface 750 ofthe recessed first fin structure 122 in the PMOS region 140. Thereafter,the method 100 removes the patterned etch mask 610 by any suitablemethod.

At operation 82, the method 100 forms S/D features in the PMOS region140 as illustrated in FIG. 8. In the depicted embodiment, the S/Dfeature 810 is formed by epitaxially growing a semiconductor material onthe top surface of the recessed first fin structure 122. The S/D feature810 may include a suitable epitaxial semiconductor material, such asgermanium (Ge), silicon (Si), gallium arsenide (GaAs), aluminum galliumarsenide (AlGaAs), silicon germanium (SiGe), gallium arsenide phosphide(GaAsP), other suitable materials, or combinations thereof. In someembodiments, the S/D feature 810 may include one or more layers ofepitaxially grown semiconductor materials. The S/D feature 810 may beformed by any suitable deposition process such as selective epitaxygrowth (SEG) or cyclic deposition and etching (CDE) epitaxy.

In some embodiments, the S/D feature 810 may include various dopants. Inthe depicted embodiment where a PMOS FinFET device is desired in thefirst region 140, the S/D feature 810 may include one or more epitaxiallayers of silicon germanium doped with a p-type dopant such as boron,germanium, indium, other p-type dopant, or combinations thereof. Anysuitable process (e.g., an ion implantation process, a diffusionprocess, an in-situ doping process, or combinations thereof) can beimplemented for doping the S/D feature 810. One or more annealingprocesses (e.g., rapid thermal annealing or laser annealing) may beperformed to activate the epitaxial structure.

At operation 84, the method 100 (FIG. 1B) removes the remaining firsthard mask layer 410 deposited over the NMOS region 150, as depicted inFIG. 9. In some embodiments, the first hard mask layer 410 can beremoved by any suitable process or processes such as, for example, bydry etch selective to the materials of the first hard mask layer 410.Subsequently, at operation 84, the method 100 (FIG. 1B) forms a secondhard mask 1010 over the various features disposed in both the NMOSregion 150 and the PMOS region 140, as depicted in FIG. 10. Similar tothe discussion above for the operation 74, the second hard mask layer1010 acts as a barrier material to protect the fins 120 from beingcontaminated by a second patterned etch mask 1110 (FIG. 11). Thereafter,at operation 88, the method 100 (FIG. 1B) forms the second patternedetch mask 1110 over the PMOS region 140, which includes the S/D feature810 and the isolation features 130 surrounding the first fin structure122, as depicted in FIG. 11. In some embodiments, the second patternedetch mask 1110 may comprise the same material as that of the firstpatterned etch mask 610.

After forming the PMOS S/D feature 810, the method 100 proceeds to formthe NMOS S/D features in the ensuing processing steps. As noted above,the NMOS S/D features generally have larger size (e.g., features mergingmultiple fins) and greater structural variations (i.e., less uniformepitaxial structures) than the PMOS S/D features. In one example,statistical variations in the sizes of NMOS S/D features areapproximately 1.5 to 2 times those of the PMOS S/D features. As aresult, forming the NMOS S/D features before forming the PMOS S/Dfeatures generally leaves a narrow processing window for the overallfabrication process. In one such example, a narrow processing window maylead to less tolerance for misalignment that may occur during subsequentlithographical, etching, and/or deposition processes. In comparison, thepresent disclosure provides methods of forming the PMOS S/D featuresbefore forming the NMOS S/D features in an effort to enlarge theprocessing window for the overall fabrication process.

At operation 90, the method 100 (FIG. 1B) recesses a portion 1210 of thesecond fin structures 124 in the NMOS region 150 while the secondpatterned etch mask 1110 covers the PMOS region 140, as depicted in FIG.12. The recessing can be implemented by any suitable process orprocesses including, for example, a dry etching process, a wet etchingprocess, an RIE process, other suitable etching process, and/orcombinations thereof. Similar to the embodiments discussed with respectto the recessing of the first fin structure 122 in the PMOS region 140,a dry etching process is implemented to recess the second fin structures124 in the NMOS region 150. Thereafter, the method 100 removes thepatterned etch mask 1110 by any suitable method.

Similar to the operation 80, the dry etching process may utilize one ormore etchant comprising fluorine, bromine, sulfur, carbon, oxygen,and/or hydrogen atoms. In some embodiments, the dry etching processimplements a mixture of etchant gasses comprising CF₄, SF₆, CH₂F₂, CHF₃,C₂F₆, Br, and/or O₂.

As depicted in FIG. 12, recessing the second fin structures 124 in theNMOS region 150 also removes portions of the isolation features 130 inthe vicinity of the second fin structures 124, resulting in a recessedregion 1230A and a recessed region 1230B in the isolation features 130.In some embodiments, the recessed region 1230A is defined by a verticaldistance 1220 between a top surface 1260 of the isolation features 130prior to the recessing process and the lowest point 1240 in the recessedregion 1230A. It is understood that the top surface 1260 in the NMOSregion 150 is approximately at the same position as the top surface 760in the PMOS region 140, and are the two highest points of the isolationfeatures 130. In some embodiments, the lowest point 1240 is at about thesame height as a top surface 1250 of the recessed second fin structures124 in the NMOS region 150. In the depicted embodiments, the verticaldistance 1220 in the NMOS region 150 is less than the vertical distance720 in the PMOS region 140, i.e., the extent of loss in the isolationfeatures 130 incurred by the recessing process is less in the NMOSregion 150 than in the PMOS region 140 when the source/drain feature 810is formed prior to the source/drain feature 1310. This may be caused bythe fact that the isolation features 130 of the PMOS region 140 areexposed to a greater amount of etchant when the first fin structure 122,which includes a single fin, is recessed than the isolation features 130of the NMOS region 150 when the second fin structures 124, which eachincludes two connected fins, are recessed. In some embodiments, a ratiobetween the vertical distance 1220 and the vertical distance 720 is fromabout 1:2 to about 2:3. Furthermore, a top surface 1250 of the recessedsecond fin structure 124 in the NMOS region 150 is above a top surface750 of the recessed first fin structure 122 in the PMOS region 140.

Still referring to FIG. 12, the isolation feature 130 between the S/Dfeature 810 and the S/D feature 1310 includes the recessed region 730B,the recessed region 1230B, and an island 170. The recessed region 730Bmay be defined by a lateral distance 1290, the recessed region 1230B maybe defined by a lateral distance 1270, and the island 170 may be definedby a lateral distance 1280. In the depicted embodiment, the island 170is disposed between the recessed profile 1230B and the recessed profile730B.

Similar to the discussion above regarding the vertical distance 1220 andthe vertical distance 720, the lateral distance of each of the recessedprofiles also reflects the extent of loss of the isolation feature 130caused by the recessing of the fin structures 122 and 124. In thedepicted embodiment, the relative magnitude of the lateral distance1270, the lateral distance 1290, and the lateral distance 1280 isaffected by the order in which the S/D feature 1310 and the S/D feature810 are formed. Specifically, because the S/D feature 1310 is larger insize and exhibits less uniformity than the S/D feature 810, forming theS/D feature 1310 (e.g., recessing the second fin structure 124) prior toforming the S/D feature 810 (e.g., recessing the first fin structure122) may leave a smaller processing window (i.e., the lateral distance1290<the lateral distance 1270) and thus less tolerance for potentialmisalignment (e.g., lithographic overlay errors) that may occur whenforming the S/D feature 810. The present disclosure provides embodimentsin which the S/D feature 810 is formed prior to forming the S/D feature1310, enlarging the processing window for forming the S/D feature 810(i.e., the lateral distance 1290 >the lateral distance 1270) andproviding enhanced control over the subsequent recessing of the secondfin structure 124 to form the S/D feature 1310. In many embodiments, thelateral distance 1290 is greater than the distance 1270. In an exemplaryembodiment, a ratio of the lateral distance 1270 to the lateral distance1290 is from about 1:5 to about 3:5, and a ratio of the lateral distance1280 to the lateral distance 1290 is less than about 1:3. In someinstances, the lateral distance 1280 may be 0.

At operation 92, the method 100 (FIG. 1B) forms S/D features 1310 in theNMOS region 150 as illustrated in FIG. 13. The process of formingepitaxially grown S/D features 1310 in the NMOS region 150 is similar tothat of the S/D feature 810 formed in the PMOS region 140, though thevarious semiconductor materials, dopants, and the final configuration ofthe epitaxial features 1310 may differ from that that of the feature 810formed in the PMOS region 140. In some embodiments, the NMOS S/Dfeatures 1310 merge together the two adjacent fins 120 of the second finstructure 124. Thus, the size of the S/D features 1310 are generallygreater than the size of the PMOS S/D feature 810, which is epitaxiallyformed over a single fin 120 (i.e., the first fin structure 122) in thePMOS region 140.

Similar to the S/D feature 810, the S/D features 1310 may includegermanium (Ge), silicon (Si), gallium arsenide (GaAs), aluminum galliumarsenide (AlGaAs), silicon germanium (SiGe), gallium arsenide phosphide(GaAsP), other suitable materials, or combinations thereof. In someembodiments, the S/D features 1310 may include one or more layers ofepitaxially grown semiconductor materials. The S/D feature 1310 may beformed by any suitable deposition process such as selective epitaxygrowth (SEG) or cyclic deposition and etching (CDE) epitaxy. Differentfrom the S/D feature 810, in the depicted embodiment where an NMOSFinFET device is desired, the S/D features 1310 may include one or moreepitaxial layers of silicon or silicon carbon, where the silicon orsilicon carbon is doped with an n-type dopant such as arsenic,phosphorus, other n-type dopants, or combinations thereof. Any suitableprocess similar to the doping, activating, and annelaing of the S/Dfeature 810 as discussed above can be implemented for the S/D features1310.

Thereafter, at operation 94, the method 100 (FIG. 1B) removes theremaining second hard mask layer 1010 from the PMOS region 140, asillustrated in FIG. 14. In some embodiments, the second hard mask layer1010 can be removed by any suitable process or processes such as, forexample, by dry etch. Accordingly, the method 100 completes theformation of the PMOS S/D features 810 followed by the formation of theNMOS S/D features 1310.

At operation 96, the method 100 (FIG. 1B) performs further steps tocomplete the fabrication of the PMOS and NMOS devices in thesemiconductor structure 200. For example, as illustrated in FIG. 15, theoperation 96 deposits a contact etch-stop layer (CESL) 1510 conformallyover the features of the PMOS region 140 and the NMOS region 150. TheCESL 1510 may comprise silicon nitride, silicon oxynitride, siliconnitride with oxygen (O) or carbon (C) elements, and/or other materials,and may be formed by CVD, PVD, ALD, or other suitable methods.

Subsequently, the operation 96 forms an interlayer dielectric (ILD)layer 1610 over the features of the PMOS region 140 and the NMOS region150, as depicted in FIG. 16. The ILD layer 1610 may include TEOS,un-doped silicate glass, or doped silicon oxide such asborophosphoslicate glass (BPSG), fused silica glass (FSG),phosphosilicate glass (PSG), boron-doped silicate glass (BSG), and/orother suitable dielectric materials. In some implementations, the ILDlayer 1610 can include a multilayer structure having multiple dielectricmaterials. The ILD layer 1610 may be formed by plasma-enhanced CVD(PECVD), flowable CVD (FCVD), or other suitable methods. The operation96 then performs one or more planarization processes, such aschemical-mechanical planarization/polishing (CMP) processes, toplanarize the top surface of the semiconductor structure 200.

The operation 96 further includes removing the dummy gate structure 160to form a gate trench (not shown) and subsequently form a high-k metalgate structure (HK MG structure; not shown) in the gate trench. The HKMG structure includes a high-k gate dielectric layer and a conductivegate electrode layer, as well as additional material layers such asinterfacial layers, capping layers, diffusion layers, barrier layers, orcombinations thereof. The high-k gate dielectric layer may include oneor more high-k dielectric materials (or one or more layers of high-kdielectric materials), such as hafnium silicon oxide (HfSiO), hafniumoxide (HfO₂), alumina (Al₂O₃), zirconium oxide (ZrO₂), lanthanum oxide(La₂O₃), titanium oxide (TiO₂), yttrium oxide (Y₂O₃), strontium titanate(SrTiO₃), or a combination thereof. The high-k gate dielectric layer maybe deposited using CVD, ALD and/or other suitable methods. Theconductive gate electrode layer may include one or more metal layers,such as work function metal (WFM) layer(s), conductive barrier layer(s),and bulk conductive layer(s). The WFM layer may be a p-type or an n-typework function layer depending on the type of the device (PMOS or NMOS),and may be, for example, TaN, NiSi, CoSi, TiN, WN, TiAl, TiAlN, TaCN,TaC, TaSiN, TaAl, TaAlC, TaN, ZrSi₂, MoSi₂, TaSi₂, NiSi₂, WN, other WFM,or combinations thereof. The bulk conductive layer may include aluminum(Al), copper (Cu), titanium (Ti), tantalum (Ta), tungsten (W), cobalt(Co), and/or other suitable materials.

Exemplary FinFET devices provided herein may be included in amicroprocessor, a memory, and/or other integrated circuit device. Insome embodiments, the FinFET devices may be a portion of an IC chip, asystem on chip (SoC), or portion thereof, that includes various passiveand active microelectronic devices such as resistors, capacitors,inductors, diodes, metal-oxide semiconductor field effect transistors(MOSFET), complementary metal-oxide semiconductor (CMOS) transistors,bipolar junction transistors (BJTs), laterally diffused MOS (LDMOS)transistors, high voltage transistors, high frequency transistors, othersuitable components, or combinations thereof. Additional features can beadded to the FinFET devices by subsequent processing steps. For example,various vertical interconnect features such as contacts and/or vias,and/or horizontal interconnect features such as lines, and multilayerinterconnect features such as metal layers can be formed over the ILDlayer 1610.

Although not intended to be limiting, one or more embodiments of thepresent disclosure offer improvements for fabricating semiconductordevices, especially FinFET devices. For example, while loss of isolationfeatures (e.g., isolation features 130) during fabrication of S/Dfeatures is commonly observed, the effects of such loss to subsequentfabrication steps vary depending upon the extent of the loss and/or thelocation of the loss, i.e., whether the loss occurs near PMOS S/Dfeatures or NMOS S/D features and the relative sizes of the loss in eachregion. Because the PMOS S/D features are generally smaller than theNMOS S/D features in size and in structural variations, allowing agreater extent of the loss to occur near the PMOS S/D features may helpmitigate the overall loss of the isolation features and increasingprocessing window of the subsequent fabrication steps. The presentdisclosure provides embodiments to accomplish this by forming the PMOSS/D features prior to forming the NMOS S/D features.

Accordingly, the present disclosure provides many different embodimentsof FinFET devices and methods of fabricating the same. In one aspect,the present disclosure provides a method of fabricating a FinFET devicethat includes providing a semiconductor substrate having a region forforming p-type metal-oxide-semiconductor (PMOS) devices and a region forforming n-type metal-oxide-semiconductor (NMOS) devices; forming a firstfin structure in the PMOS region and a second fin structure in the NMOSregion, the fin structures being separated by isolation features;recessing the first fin structure; epitaxially growing a firstsource/drain feature on the recessed first fin structure; subsequently,recessing the second fin structure; and epitaxially growing a secondsource/drain feature on the recesses second fin structure.

In some embodiments, the first fin structure includes one fin and thesecond fin structure includes two fins connected at bottom of the twofins. In further embodiments, the second source/drain feature in theNMOS region merges the fins of the second fin structure together.

In some embodiments, recessing the first fin structure includes forminga first hard mask layer over the PMOS region and the NMOS region;forming a first patterned etch mask over the NMOS region therebyexposing the PMOS region; and recessing the first fin structure, whichin turn removes portions of the isolation features in the PMOS regionsuch that the isolation features have a first depth with respect to atop surface of the isolation features prior to the recessing.

In some embodiments, epitaxially growing the first source/drain featureincludes epitaxially growing a p-type epitaxial semiconductor structureon the recessed first fin structure; removing the first hard mask layerfrom the NMOS region; and forming a second hard mask layer over the PMOSregion and the NMOS region.

In some embodiments, recessing the second fin structure includes forminga second patterned etch mask over the PMOS region to expose the NMOSregion, and recessing the second fin structure, such that the recessingremoves portions of the isolation features in the second region suchthat the isolation features have a second depth with respect to a topsurface of the isolation features prior to the recessing. In a furtherembodiment, the second depth is less than the first depth. In someembodiments, recessing the second fin structure results in the secondfin structure having a top surface above a top surface of the first finstructure.

In some embodiments, epitaxially growing the second source/drain featureincludes epitaxially growing an n-type epitaxial semiconductor structureon the recessed second fin structure, and removing the second hard masklayer from the PMOS region.

In some embodiments, recessing the first fin structure and the recessingof the second fin structure forms a first recessed region and a secondrecessed region in the isolation features, respectively, the firstrecess region and the second recess region being formed between thefirst fin structure and the second fin structure. In furtherembodiments, a lateral distance of the first recessed region is greaterthan a lateral distance of the second recessed region.

In another aspect, the present disclosure provides a method offabricating a FinFET device that includes providing a first finstructure on a semiconductor substrate for forming p-typemetal-oxide-semiconductor (PMOS) devices and a second fin structure onthe semiconductor substrate for forming n-type metal-oxide-semiconductor(NMOS) devices, the first fin structure and the second fin structurebeing separated by isolation features; forming a first hard mask layerover the first fin structure, the second fin structure, and theisolation features; removing a portion of the first fin structure toform a recessed first fin structure; forming a first source/drainfeature on a top surface of the recessed first fin structure; removingthe first hard mask layer from the second fin structure and theisolation features surrounding it; subsequently, forming a second hardmask layer over the first source/drain feature, the second finstructure, and the isolation features; subsequently, removing a portionof the second fin structure to form a recessed second fin structure;forming a second source/drain feature on a top surface of the recessedsecond fin structure; and subsequently, removing the second hard masklayer from the first fin structure and the isolation featuressurrounding it.

In some embodiments, the first fin structure comprises one fin and thesecond fin structure comprises two fins connected at bottom of the twofins. In a further embodiment, forming the second source/drain featuremerges the two fins of the second fin structure. In yet anotherembodiment, a top surface of the recessed first fin structure is below atop surface of the recessed second fin structure. In some embodiments,removing the portion of the first fin structure comprises removingisolation features in the first region to form a first recessed region,wherein removing the portion of the second fin structure comprisesremoving isolation features in the second region to form a secondrecessed region, and wherein a lowest point of the first recessed regionand the second recessed region is closer to the first source/drainfeature than to the second source/drain feature. In some embodiments,removing the portion of the first fin structure comprises removingisolation features in the first region to form a third recessed region,and removing the portion of the second fin structure comprises removingisolation features in the second region to form a fourth recessedregion. In further embodiments, the third recessed region and the fourthrecessed region are formed in a space between the first source/drainfeature and the second source/drain feature and are separated by anisland of the isolation features.

In yet another aspect, the present disclosure provides an exemplaryFinFET device that includes a semiconductor substrate having a regionfor forming p-type metal-oxide-semiconductor (PMOS) devices and a regionfor forming n-type metal-oxide-semiconductor (NMOS) devices; asource/drain feature over a fin structure in the PMOS region, thesource/drain feature comprising a p-type epitaxial structure; anothersource/drain feature over a fin structure in the NMOS region, thesource/drain feature comprising an n-type source/drain structure; andisolation features between the first source/drain feature and the secondsource/drain feature. In some embodiments, the isolation featuresincludes a first portion adjacent to the first source/drain feature, asecond recessed portion adjacent to the second source/drain feature, anda third portion disposed between the first portion and the secondportion. In further embodiments, a lateral distance of the first portionis greater than a lateral distance of the second portion.

In some embodiments, the fin structure in the PMOS region comprises onefin and the fin structure in the NMOS region comprises two fins. In afurther embodiment, the source/drain features formed in the NMOS regionmerges the fins of the fin structure in the NMOS region together. Insome embodiments, a distance between a lowest point and a highest pointof the first portion of the isolation features is greater than adistance between a lowest point and a highest point of the secondportion of the isolation features.

In some embodiments, a ratio of the lateral distance of the firstportion of the isolation features to the lateral distance of the secondportion of the isolation features is between about 1:5 and about 3:5.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor structure, comprising: asemiconductor substrate having a first region for forming p-typemetal-oxide-semiconductor (PMOS) devices and a second region for formingn-type metal-oxide-semiconductor (NMOS) devices; a first source/drainfeature over a first fin structure in the first region, the firstsource/drain feature including a p-type epitaxial structure; a secondsource/drain feature over a second fin structure in the second region,the second source/drain feature including an n-type source/drainstructure; and isolation features between the first source/drain featureand the second source/drain feature, the isolation features including afirst portion adjacent to the first source/drain feature, a secondportion adjacent to the second source/drain feature, and a third portionbetween the first portion and the second portion, wherein a width of thefirst portion is greater than a width of the second portion.
 2. Thesemiconductor structure of claim 1, wherein the first fin structureincludes one fin and the second fin structure includes two fins.
 3. Thesemiconductor structure of claim 2, wherein the second source/drainfeature merges the two fins of the second fin structure together.
 4. Thesemiconductor structure of claim 1, wherein a vertical distance betweena lowest point and a highest point of the first portion of the isolationfeatures is greater than a vertical distance between a lowest point anda highest point of the second portion of the isolation features.
 5. Thesemiconductor structure of claim 1, wherein a ratio of the width of thefirst portion of the isolation features to the width of the secondportion of the isolation features is between about 1:5 and about 3:5. 6.The semiconductor structure of claim 1, wherein a top surface of thefirst fin structure is below a top surface of the second fin structure.7. The semiconductor structure of claim 1, wherein a width of the thirdportion is less than the width of the first portion.
 8. A semiconductorstructure, comprising: a first fin structure disposed in a first regionof a semiconductor substrate for forming a p-typemetal-oxide-semiconductor (PMOS) device; a p-type source/drain (S/D)feature disposed on a top surface of the first fin structure; a secondfin structure disposed in a second region of the semiconductor substratefor forming an n-type metal-oxide-semiconductor (NMOS) device, whereinthe second region is adjacent to the first region, and wherein the topsurface of the second fin structure is above the top surface of thefirst fin structure; an n-type S/D feature disposed on a top surface ofthe second fin structure; and a dielectric layer separating the firstfin structure from the second fin structure.
 9. The semiconductorstructure of claim 8, wherein the first fin structure includes a singlefin, and wherein the second fin structure includes two fins connected attheir bottom portions.
 10. The semiconductor structure of claim 9,wherein the n-type S/D feature merges the two fins of the second finstructure together.
 11. The semiconductor structure of claim 8, whereina size of the p-type S/D feature is smaller than a size of the n-typeS/D feature.
 12. The semiconductor structure of claim 8, wherein alowest point of the dielectric layer contacts a bottom portion of thep-type S/D feature.
 13. The semiconductor structure of claim 8, whereina highest point of the dielectric layer is laterally separated from thetop surface of the first fin structure by a first distance, wherein thetop surface of the dielectric layer is laterally separated from the topsurface of the second fin structure by a second distance, and whereinthe first distance is greater than the second distance.
 14. Asemiconductor structure, comprising: a semiconductor substrate; a firstfin structure disposed over the semiconductor substrate; a firstsource/drain (S/D) feature disposed on the first fin structure, whereinthe first S/D feature includes a p-type epitaxial material; a second finstructure disposed over the semiconductor substrate and adjacent to thefirst fin structure; a second S/D feature disposed on the second finstructure, wherein the second S/D feature includes an n-type epitaxialmaterial; and an isolation structure separating the first and the secondfin structures, wherein the isolation structure includes a first regionsurrounding the first fin structure, a second region surrounding thesecond fin structure, and an island region disposed between the firstand the second regions, and wherein a lowest point of the first regionis below a lowest point of the second region.
 15. The semiconductorstructure of claim 14, further comprising an etch-stop layer disposedconformally over the first and the second S/D features and the isolationstructure.
 16. The semiconductor structure of claim 14, wherein theisland region is disposed above the lowest point of the second region.17. The semiconductor structure of claim 14, wherein the island regionis laterally separated from a bottom surface of the first S/D feature bya first distance, wherein the island region is laterally separated froma bottom surface of the second S/D feature by a second distance, andwherein the second distance is less than the first distance.
 18. Thesemiconductor structure of claim 17, wherein a top surface of the islandregion laterally expands a third distance, and wherein the thirddistance is less than the first distance.
 19. The semiconductorstructure of claim 18, wherein a ratio of the third distance to thefirst distance is greater than a ratio of the second distance to thefirst distance.
 20. The semiconductor structure of claim 18, wherein aratio of the second distance to the first distance is greater than aratio of the third distance to the first distance.